1. Field of the Invention
The present invention relates to a manufacturing method of a circuit substrate to form an electronic circuit on a surface of a base member, a circuit substrate manufactured by the method and a manufacturing device of the circuit substrate.
2. Description of Related Art
Recently, a technique for forming an electronic circuit on a surface of a base member by jetting an ink including conductive fine particles, for example, through a thermal type of or a piezo type of solution jetting device, has been developed. The technique is, for example, disclosed in Patent Document 1 (Unexamined Japanese Patent Publication No. Tokukaihei-9-320363 (1997)) and Patent Document 2 (Unexamined Japanese Patent Publication No. Tokukai-2002-134878). Further, a technique for forming an electronic circuit including condensers and resistors on a surface of a base member by selectively jetting an ink including conductive or insulating fine particles through a piezo type of solution jetting device has been developed (Unexamined Japanese Patent Publication No. 11-274671 (1999)).
According to these techniques, a circuit substrate having an electronic circuit with a line width of tens μm can be made.
In various electronic products such as a portable phone, a video camera and the like which are desired to be miniaturized and have high performance, the circuit substrate is desired to be further miniaturized and have a further high performance. Therefore, the formation of the electronic circuit having a further fine line width is desired.
However, there are following problems in the earlier developments or prior arts, and the problems prevent formation of fine line width in the electronic circuit.
(1) Stability Problem of Formation of a Fine Liquid Drop:
Because the diameter of a nozzle is large, the shape of a liquid drop jetted from the nozzle is not stable.
(2) Insufficient Accuracy in the Position of the Jetted Fine Liquid Drop to be Received on the Circuit Substrate:
The kinetic energy given to a liquid drop jetted from a nozzle is proportional to the third power of a liquid drop diameter. Therefore, a fine liquid drop has no sufficient kinetic energy to resist the air disturbance, so that the fine liquid drop flying toward the circuit substrate is disturbed by the air convection. As a result, it is difficult that the fine liquid drop accurately arrives at an aimed position of the circuit substrate. Further, as the liquid drop is finer, the effect of the surface tension of the liquid drop is increased, the vapor pressure of the liquid drop is heightened, and an amount of vaporized liquid is increased. Therefore, the weight of the fine liquid drop is considerably decreased during the flying of the drop, and it is difficult that the fine liquid drop merely maintains a drop shape. Therefore, the high positional accuracy of the arriving fine liquid drop on the circuit substrate contradicts the formation of the finer liquid drop, and it is difficult to obtain the fine liquid drop correctly arriving at a predetermined position.
Further, an electrostatic suction type of solution jetting device is used to jet liquid drops on the surface of the substrate and is disclosed in both Patent Document 4 (Unexamined Japanese Patent Publication No. Tokukaihei-8-238774 (1996)) and Patent Document 5 (Unexamined Japanese Patent Publication No. Tokukai-2000-127410).
However, the solution jetting devices of the documents have the same problems as those described above, and there are following additional problems.
(3) Applied High Voltage
In the electrostatic suction type of solution jetting devices, charge is concentrated in the center of an end portion (hereinafter, may be referred to a meniscus area) of a solution held in a nozzle to swell the meniscus area. The swelled meniscus area is formed in a hemispherical shape. A curvature radius of a tailor cone end of the swelled meniscus area is determined according to the amount of concentrated charge, and an electrostatic force is induced in the meniscus area according to the electric field strength generated by the concentrated charge. When the electrostatic force is larger than the force caused by the surface tension of the solution, a liquid drop is separated from the solution of the meniscus area.
A maximum amount of concentrated charge in the meniscus area is determined by physical properties (particularly, surface tension) and a meniscus curvature radius of the solution. Therefore, a size of the minimum liquid drop is determined by the physical properties such as surface tension of the solution and the electric field strength induced in the meniscus area.
The surface tension of a solvent including a solute is generally inclined to be lower than that of a pure solvent. Because an actual solution comprises a solvent and various solutes, it is difficult to heighten the surface tension of the actual solution. Accordingly, it has been thought that the surface tension of the solution is constant, a method for minifying the size of the liquid drop by increasing the electric field strength has been adopted in the earlier development.
Therefore, in the solution jetting devices of the documents, a highly-strengthened electric field is formed in the meniscus area considerably wider than the projective area of a liquid drop to concentrate charges at the center of the meniscus area, so that the liquid drop is jetted by the electrostatic force which is induced by the concentrated charges and the formed electric field. In this case, it is required to apply a very high voltage of around 2000V to the solution. Therefore, a problem that the driving control of the devices is difficult and the solution jetting devices may not be safely operated, has arisen.
(4) Response of Jet
In the solution jetting devices, because a highly-strengthened electric field is formed in the meniscus area considerably wider than the projective area of a liquid drop to concentrate charges at the center of the meniscus area, so that the liquid drop is jetted by the electrostatic force which is induced by the concentrated charges and the formed electric field, there has been a problem that the charge moving time required for moving the charges to the center of the meniscus area exerts effect on the response performance of the jet of the liquid drop and on formation speed of a liquid drop pattern.